Feasibility of his bundle pacing as an alternative pacing site: measurement of his refractoriness

Direct pacing of the His bundle has been proposed for permanent pacing to maintain physiological synchrony of ventricular activation. Measurement of His bundle refractoriness may be useful in predicting suitability of this technique in an individual. We sought to determine whether this could be measured consistently in patients, defining a normal range.

His bundle pacing was performed in 20 consecutive patients (mean age 44.6 +/- 19.5, 5 male) undergoing electrophysiology study. Incremental and extrastimulus testing were performed from the His region to determine effective and functional refractory periods of the His bundle.

Consistent His capture was possible in 18 of 20 (90%) patients studied. Extrastimulus testing from the His region at a drive cycle length of 600 msec was successful in all of these patients. With loss of His capture, QRS duration prolonged 32%, and stimulus to atrial electrogram interval prolonged 49.6 +/-16.3 msec. The effective refractory periods at drive cycle lengths 600, 500, and 400 msec were 407 +/- 70 msec, 320 +/- 39 msec, and 336 +/- 54 msec, respectively. Corresponding functional refractory periods were 414 +/- 62, 371 +/- 52, and 329 +/- 32. Consistent capture with incremental His pacing was possible in 50% of patients, and 1:1 His capture was lost at mean cycle length 408 +/-93 msec.

His refractory periods can be determined consistently in unselected individuals undergoing electrophysiological studies. Measurement of HERP and HFRP may prove useful in assessing the suitability of the His bundle for permanent pacing.